Dual surface density baffle for clarifier tank

ABSTRACT

A baffle system for use in a clarifier tank, having a tank bottom and a periphery and a substantially vertical peripheral wall bounding the interior of the tank, has a plurality of baffles mounted on the peripheral wall of the clarifier tank. each baffle has an upper baffle surface with a lower end and an upper end. The upper end of the upper baffle portion is coupled to the side wall of the clarifier tank wall. The lower end of the upper baffle portion is disposed. at a substantially 60° angle away from the side wall of the clarifier tank such that the upper baffle surface slopes downwardly and away from the side wall.

RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.12/423,181 filed on Apr. 14, 2009, now U.S. Pat. No. 7,963,403, which inturn claims the benefit of priority from U.S. Provisional PatentApplication No. 61/125,275, field on Apr. 23, 2008; U.S. ProvisionalPatent Application No. 61/206,039, filed on Jan. 26, 2009; U.S.Provisional Patent Application No. 61/206,574, filed on Jan. 30, 2009,and U.S. Provisional Patent Application No. 61/196,405, filed on Oct.15, 2008 the entirety of which are incorporated by reference.

BACKGROUND

1. Field of the Invention

This application relates to a baffle and baffle system for use in asolids-precipitating clarifier tank. More particularly, the applicationrelates to a baffle and baffle system having a plurality ofinter-engaged individual baffles secured to the clarifier lankperipheral wall.

2. Prior Art Discussion

Baffle devices, also known in the art as a lamella gravity separators orsettlers, are used in clarifier tanks for waste treatment forgravitationally separating suspended solids from solids containingcarrier liquid or fluid suspensions. The clarifier tanks, with whichsuch baffles are typically used, are circular or rectangularlyconfigured tanks in which a centrally mounted radially extending arm isslowly moved or rotated about the tank at or proximate the surface ofthe carrier liquid.

Specifically, in waste water treatment facilities utilizing secondaryclarifiers, the clarifier's effectiveness in removing solids is perhapsthe most important factor in establishing the final effluent quality ofthe facility.

A major deterrent to effective removal is the presence of sludge densitycurrents which cause hydraulic short circuits within the tank. Theseshort circuits, in turn, allow solids concentrations to unintentionallybypass the tank's clarification volume and enter the effluent. In theprior art, peripheral baffles are attached to the tank wall and directeddownward at an angle into the tank. These baffles help to minimize thedensity currents and properly redirect the flow of solids away from theeffluent and into the main clarification volume (center) of the tank.

However, although these density baffle systems work to significantlyreduce solids from entering the effluent, under greater load conditionsthese baffle systems occasionally fail, allowing for the above describedshort circuits.

SUMMARY

The present arrangement overcomes the drawbacks associated with theprior art providing for a dual surface baffle, combining an inclinedupper surface, similar to the prior art design, with a lower bafflesurface that mirrors the first, inclined back toward the tank wall,forming a wedge-shaped dual surface baffle. Such an arrangement allowsthe lower portion to be retrofitted to any existing downwardly angledbaffles, upgrading it to the presently described dual surfaceconfiguration. In one configuration, the upper and lower inclinedsurfaces of the baffle are set 30° degrees off from a line perpendicularto the tank wall (i.e. 60° degrees from the wall itself). Such aconfiguration results in a smaller tank wall footprint” and also allowsthe same amount of baffle construction material to reach further intothe center of the clarifier tank.

According to this embodiment, the dual surface baffle reduces clarifiereffluent solids to a far greater extent than prior art designs; improvesfunctionality as in larger sized clarifiers: and improves effectivenesswith increased effluent flow.

In one arrangement. the dual surface density current baffle reduceseffluent solids (TSS—Total Suspended Solids) by as much as 80% overprior art designs. The dual surface baffle may be advantageouslyutilized in larger clarifiers (80 foot diameter and up) and thoseclarifiers that operate at higher effluent flows, including clarifiersin combined sewer configurations. Such a design redirects the densitycurrent, just above the blanket and then lifting upward as they near thetank wall, back toward the center of the tank.

BRIEF DESCRIPTION OF THE DRAWING

The present invention can be best understood through the followingdescription and accompanying drawings, wherein:

FIG. 1 shows a dual surface baffle as installed on a clarifier tank wallin accordance with one embodiment of the present invention:

FIG. 2 shows a dual surface baffle in accordance with one embodiment ofthe present invention;

FIG. 3 shows a three dimensional depiction of a dual surface baffle inaccordance with one embodiment of the present invention;

FIG. 4 shows a plurality of dual surface baffles in accordance with oneembodiment of the present invention as each mounted on a clarified tankwall; and

FIG. 5 shows a surface baffle with side bracket in accordance with oneembodiment of the present invention;

FIG. 6 is a relative effluent concentration comparison chart inaccordance with one embodiment; and

FIG. 7 is a relative effluent concentration comparison chart inaccordance with one embodiment.

DETAILED DESCRIPTION

In one arrangement. shown in FIG. 1, dual surface density current baffle10 is shown attached to a tank wall T. Density baffle 10 is made from anupper baffle surface 12 and second lower baffle surface 14. Upper bafflesurface 12 slopes downwardly away from wall T towards the center of thetank and lower baffle surface 14 is positioned below upper surface 12,sloping upwardly away from wall T towards the center of the tank. Upperand lower baffle surfaces 12 and 14 meet a central plane 24. parallel towall T. Typically, central plane 24 is approximately 3 inches in lengthto provide a substantial connection surface between upper and lowersurfaces 12 and 14, but it is not limited in this respect. Upper bafflesurfaces 12 and lower baffle surfaces 14 are connected to tank wall Tvia upper and lower mounting flanges 16 and 20 respectively.

In one arrangement as shown in FIGS. 2 and 3, upper mounting flange 16incorporates a series of integrally molded vent openings 18. Lowermounting flange 20 may also include a corresponding series of 2″ widevents 22 or similar openings at the bottom of baffle 10 allowing solidflow to enter and leave the interior of baffle 10 so as not to betrapped, and also provide a means of cleaning baffle 10, if necessary.when the clarifier is dewatered for annual maintenance.

As shown in FIG. 5, density baffle 10 is shown having upper bafflesurface 12 which slopes downwardly and away from wall T (not shown)towards the center of the tank. Additionally, density baffle 10 isprovided with an integrally molded side bracket 26 which providessupport and rigidity for density baffle 10. As well, an integrallymolded side bracket flange 28 is shown and is provided to maintainvertical support for side bracket 26 and upper baffle surface 12. Inthis way, when the plural baffles 10 are disposed in end to end relationabout the peripheral tank wall, such that the second lateral end of thepanel member of each baffle is secured to the end bracket of thenext-adjacent baffle, whereby each end bracket 26 supports the bafflesurface 12 of each set of two immediate-adjacent baffles on theperipheral wall as set forth in U.S. Pat. No. 5,252,205, the contents ofwhich are incorporated herein by reference. Although FIG. 5 shows endbracket 26 integrally molded to baffle surface 12, it is to beunderstood that end bracket 26 may be separate and apart from bafflesurface 12 and installed as a two piece assembly.

In one embodiment, as shown in FIG. 2, typically, the baffles areinclined at substantially 60 degrees measured from the vertical tankwall T. Such an arrangement. with the 60° inclination angles betweenupper and lower baffle surfaces 12 and 14 and wall T of the clarifiertank, offers improved baffle performance over the more common prior art45° angle.

One additional advantage of the 60° angle arrangement shown in FIG. 2,with respect to prior art arrangements is that it results in a smallervertical footprint on the tank wall while still achieving the desiredhorizontal projection into the tank. For example, the equation used todetermine the desired horizontal projection depth of baffle 10 away fromwall T into the tank is:HP=18+a(D−30)

D=diameter of the tank in feet:

a=coefficient multiplier

For a long time, the “a” coefficient was set to 0.2 inches per footwhich for a 100 foot diameter clarifier tank would set a desiredhorizontal baffle projection of approximately 32 inches. More recently,it has been suggested that an “a” coefficient of 0.3 inches per foot (orgreater) be used resulting in a 39 inch horizontal projection.

With prior art density baffles set at 45° degree angles, this additionalprojection requires a significant amount of baffle material and cost aswell as a larger tank wall footprint. The present invention, by settingthe deflection angle of upper and lower baffle to 30° from horizontal(60° from the wall T), is able to achieve greater horizontal projectionfor all size tanks, such as substantially 39 inches for a 100 foot tank,less material and a smaller tank wall footprint, while still maintainingthe desirable amount of protection from allowing solids to escape intothe effluent. As shown in FIG. 2, horizontal projection h is noted asthe distance between the tank wall and central plane 24.

In another embodiment, when the lower surface 14 is retro-fitted to anexisting baffle, it is likely that the upper surface 12 of such anexisting baffle is longer and inclined at 45° degrees. In such aninstance, a hybrid design may be utilized where the Lower surface 14 isinclined at 60° degrees from wall T and is of the length necessary tomeet the existing baffle.

It is understood that the above identified angles for baffle surfaces 12and 14 are exemplary only and are in no way intended to limit the scopeof the application. Any substantially similar angles used with theconjoining dual surface baffle 10 are within the contemplation of thisapplication.

In order to test the efficacy of dual surface baffle 10 described above,it has been tested under similar conditions to the prior art singlesurface (downward sloping) baffle designs. Exemplary computations werecarried out with a commercial Computational Fluid Dynamics (CFD) programcalled FLOW.3DTM. Simulation testing of dual surface baffle 10 includesdesign testing against several different fluid motion equationsincluding the transient, three-dimensional, Navier-Stokes equations[three equations], an equation of fluid continuity [—a condition ofincompressibility], a two-equation turbulence model [two equations], anda drift-flux equation [—represent solids settling]. Such computationsmay use a structured, rectangular, mesh, and a Fractional Area/VolumeObstacle Representation (FAVOR) method to account for tank and bafflegeometry.

The following descriptions of exemplary testing results showing theefficacy of dual surface baffle 10 versus prior art single surfacebaffles. In the tests, fluid was initially motionless in the clarifiersand steady flow conditions were modeled (i.e.. flow rates specified atthe clarifier inlet and outlets were increased linearly from zero untilthe desired flow condition was achieved). In most cases, sediment solidsconcentrations associated with the steady-flow conditions were reportedand used to evaluate the effectiveness of the different baffle designs.

Surface Overflow Rate (SOR) is a measure of the volume of input materialand processed through the clarifier in a 24 hour period, divided by thesurface area of the clarifier. For example, in the case of the 100 footdiameter clarifier, the surface area of the clarifier is 7854 squarefeet. If the SOR is 1300, the input to the clarifier is 10,200,000gallons per day, commonly referred to as 10.2 MGD.

The following Table I shows the test results for the prior art baffleversus dual surface baffle 10 as described above. The test was set for70 foot to 100 foot diameter clarifiers with the SOR fixed at 1300gpdlft2 and with the distance between the blanket and the top of thesludge blanket also being fixed.

TABLE 1 Relative Effluent TSS, Stamford Baffle and Dual Surface Baffle70 ft 80 ft 90 ft 100 ft Stamford Baffle .40 .35 .35 .34 Dual SurfaceBaffle .66 .70 .72 .80

Each entry in Table 1 is the ratio of the effluent TSS (Total SuspendedSolid) concentration with no baffle to the effluent TSS concentrationwith the baffle. In the 70-foot clarifier, the prior art baffle reducedeffluent TSS by 40% as compared to an unbaffled” control case. Under thesame control conditions, baffle 10 reduced the TSS by 66%. The resultsfor the Dual Surface Baffle show continued improvement as clarifierdiameter increases.

Supporting the fact that these test results are applicable under workingconditions. the test results for the prior art designs are substantiallyconsistent with measurements obtained from actual installations.

Another issue with prior art baffles used in clarifier tanks is thatthey tend not to be effective in clarifiers operating at low flowbecause there are no density currents affecting flow. The formation andenergy of density currents in a clarifier are largely dependent on theinfluent flow, the depth of the clarifier and the depth of the blanket.In the present instances, the simulated clarifier configurationsemployed SOR in the range of 400-600. the density currents lacksufficient energy to carry any lighter solids up the clarifier wall.Time-series flow' simulations show that these currents may reach theclarifier wall only to fall back on themselves without effecting TSS. Asthe flow increases, the density currents increase and blanket depthbuilds with a greater volume of unsettled solids at the top of theblanket. At this point the velocity of the density currents increases,they begin to transport lighter solids, and the density current bafflesbegin to function.

As shown in Tables 2 and 3, prior art baffles are compared against dualsurface baffle 10 in simulated 70 foot clarifier and 100-foot claritiersacross a range of surface overflow rates from 400 to 1300. The resultsfor the two baffles were nearly identical through 700-800. Beyond that,their performance began to diverge as shown in both Tables 2 and 3.

In the 70-foot diameter clarifier, shown in FIG. 6, the performance ofthe two baffles begins to diverge at about 800. At that point, the testresults suggest that the prior art baffles designs reduce 50% moresolids than the no-baffle control case. As with the above test results,these results are consistent with measurements from installations thatemploy prior art baffles, lending veracity to the testing conditions.

As the overflow rate increases by nearly 100% to 1300, the performanceof the prior art baffle drops by roughly 10%-15%. This suggests that theprior art baffle designs do not enable the clarifier to operate athigher flow and maintain TSS up to some limit. On the other hand,lending to the dual surface design of baffle 10, the performance remainsconstant at 50% through 900 and then actually increases to 65% at 1300,roughly the inverse of the prior art designs.

In the 100-foot clarifier shown in FIG. 7 both baffles function alike upto roughly 700, and then performance diverges rapidly. The prior artdesign performance follows a similar pattern to that of the 70-footclarifier, decreasing with increased SOR and ending up at nearly thesame level. On the other hand, the performance of dual surface baffle 10continues to improve with increased SOR. particularly through the rangeof 900 to 1200.

It is noted that the baffle performance is sensitive to the distancebetween the baffle and the sludge blanket. In prior art arrangements thetypical distance appears to be two feet from the bottom of the baffle tothe top of the blanket. For the dual surface baffle 10, it is desirableto arrange it against tank wall T so that the blanket is at the lowpoint of baffle 10.

The dual surface density baffle 10 offers significantly betterperformance than the prior art designs in larger tanks and treatmentplant operations that are subject to high flows, including facilitieswith combined sewer configurations. The incorporation of baffle 10enables treatment plants to treat significantly higher flows through theclarifier while maintaining allowable levels of TSS. The application ofbaffle 10 may eliminate the need for tertiary processing in some cases.

In one arrangement, as shown in FIG. 4, the performance of bathe 10 hasbeen determined to depend, at least in part on distance between thebottom of the lower surface 14 (measured from where lower surface isconnected to tank wall T) and the top of the sludge blanket. The sludgeblanket refers to the settled solids accumulated at the bottom of thetank. This sludge blanket typically is between I and 6 feet deep (ie.from the bottom of the tank). For the purposes of illustration, thesludge blanket in FIG. 4 is set at 2 feet from the bottom of the tank.

In the arrangement of the present invention, baffle 10 is positionedsubstantially 2 feet from the top of the sludge blanket (ie. 4 feet fromthe bottom of the tank). It is understood that this measurement isexemplary, and that adjustments to this positioning of baffle 10 alongthe height of tank wall T are within the contemplation of thisapplication.

While only certain features of the invention have been illustrated anddescribed herein, many modifications, substitutions, changes orequivalents will now occur to those skilled in the art. It is therefore,to be understood that this application is intended to cover all suchmodifications and changes that fall within the true spirit of theinvention.

1. A baffle system in a clarifier tank having a tank bottom and aperiphery and a substantially vertical peripheral wall bounding theinterior of the tank, said baffle system comprising: a plurality ofupper baffle surfaces, each mounted on the peripheral wall of theclarifier tank, said upper baffle surfaces each having a lower end andan upper end, the upper end of said upper baffle surfaces being coupledto the side wall of the clarifier tank wall, the lower end of said upperbaffle surfaces being disposed at a substantially 60° angle away fromthe side wall of the clarifier tank such that said upper baffle surfaceseach slope downwardly and away from the side wall forming asubstantially continuous arrangement around the peripheral wall of theclarifier tank; a plurality of lower baffle surfaces, each of whichsubstantially correspond to a corresponding one of said plurality ofupper baffle surfaces, said lower baffles surfaces each having a lowerend and an upper end, the upper end of said lower baffle surfaces beingcoupled to the lower ends of substantially corresponding upper bafflesurfaces, and with said lower ends of said lower baffle surfaces beingdisposed at a 60° angle to the side wall of the clarifier tank, suchthat said lower baffle surfaces slope upwardly and away from the sidewall said combination of said upper baffle surfaces and said coupledlower baffle surfaces forming a substantially continuous dosed densitycurrent baffle around the peripheral wall of the clarifier tank.
 2. Thebaffle system of claim 1, where the horizontal projection of saiddensity current baffle into the center of the tank is determined usingthe following equation:HP=18+a(D−30) D=diameter of the tank in feet: a=coefficient multiplierwith the coefficient “a” is set to 0.3 inches per foot.
 3. The bafflesystem of claim 2, wherein said has a diameter of tank of 100 ftdiameter, resulting in a horizontal projection of 39 inches.
 4. Thebaffle system of claim 1, wherein each of said upper and lower bafflesurfaces, further comprise mounting flanges secured to the peripheralwall for securing said baffle surfaces to the peripheral wall of theclarifier tank.
 5. The baffle system of claim 1, wherein each of saidupper baffle surfaces further comprise vent openings integrally moldedwithin said mounting flange.
 6. The baffle system of claim 1, whereineach of said baffle surfaces are molded of a reinforced fiberglasscomposite.
 7. The baffle system of claim 6, wherein each of said bafflesurfaces is integrally molded of a reinforced fiberglass composite. 8.The baffle system of claim 7, wherein each of said baffle surfaces,further comprise mounting flanges secured to the peripheral wall forsecuring said baffle surfaces to the peripheral wall of the clarifiertank.
 9. The baffle system of claim 1, wherein said density currentbaffle is positioned substantially 2 feet from the top of a sludgeblanket of the tank, measured from where the bottom surface of saiddensity current baffle is attached to the side wall of the tank.
 10. Thebaffle system of claim 1, wherein said upper baffle surfaces furthercomprise an end bracket for supporting said upper baffle surfaces alonga vertical axis on said tank wall.
 11. The baffle system of claim 10,wherein said upper baffle surfaces and said end brackets are integrallymolded.
 12. The baffle system of claim 11, wherein each of said endbrackets, further comprise mounting flanges secured along a verticalaxis to the peripheral wall for securing said baffle surfaces to theperipheral wall of the clarifier tank.